To be effective, a radiation therapy protocol should control the cumulative dose delivered to a tumor to better than 5%, while minimizing the dose to the surrounding tissue. Presently, there exists no practical means for actually measuring in vivo, the cumulative dose received by either the tumor or the surrounding tissue. Both TLD's, which must be removed from the body to be read, and miniature active radiation detectors, with their transcutaneous wires, have found very limited application because of their readout procedures. We are proposing to develop an implantable, passive dosimeter which can be read remotely without transcutaneous wires. When fully developed, the devices will be only slightly larger than grains of rice and could be implanted with a biopsy needle in both the tumor and the surrounding tissue prior to the course of therapy. The new dosimeters are designed to exhibit a linear change in properties with the cumulative radiation dose. By using a remote readout technique similar to those used by retail stores to prevent shoplifting, the devices could be nondestructively read at will and could provide the data needed for accurate irradiation of tumors located in critical areas.